usb: gadget: u_serial: Implement remote wakeup capability

Implement the remote wakeup capability for u_serial. The newly added
function gserial_wakeup_host() wakes up the host when there is some
data to be sent while the device is suspended. Add gser_get_status()
callbacks to advertise f_serial interface as function wakeup capable.

Signed-off-by: Prashanth K <prashanth.k@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250424121142.4180241-1-prashanth.k@oss.qualcomm.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>